The present invention relates to a novel, thermoformable multi-layer film useful in goods packaging, especially foodstuffs. The present invention more particularly relates to thermoplastic multi-layer films having good formability during deep-draw thermoforming and resistance to abrasion, puncture, and impact, especially at low temperatures.
It is common practice to package articles, such as food products, in thermoplastic films to protect the product from abrasion and contamination. Thermoplastics also provide a convenient and durable package for further processing, transportation, and ultimate sale to an end user. Current marketing and distribution practices in the sale of foodstuffs, particularly meat products, have put an increasing demand on the packaging materials to provide needed shelf life.
Thermoformable plastic films with low oxygen transmission rates are especially useful when packaging oxygen-sensitive products including meats. Color retention of the product and extended shelf life are advantageous features of low oxygen permeability. It is also desirable to provide a packaging material that, after the thermoforming operation, will maintain a tight package appearance.
Special problems arise when large amounts of food, such as three kilograms of frankfurters, are packaged in a thermoformed film. Bulky or heavy foodstuffs exert greater stresses upon the packaging film than the smaller packages common in the consumer market, especially if the package is dropped. Problems also arise with the use of in-line chillers following package closure because these chillers subject the packaged product to repeated impact and abrasion.
Packaging films fail when oxygen enters the package due to a hole in the packaging film. Such a hole may arise in numerous ways including sealing failure, puncture, abrasion, or rupture. In the current application, the combination of product bulk, weight, cooling to 0° C., impact, and abrasion resulted in an extremely high incidence of film failure in traditional films. In many instances, the hole is too small to be observed by the naked eye and is only apparent when the package no longer tightly fits the product because of air leakage or when the package is opened by the consumer to reveal spoiled product.
During the sealing of three-kilogram frankfurter packages using available films only 2% to 5% of the packages appeared to have failed during the sealing process. Within 24 hours of sealing, however, 10% to 15% of the packages had failed. When the packages reached the consumer, 40% to 50% of the packages had failed. This high failure rate of commercially available thermoforming films prompted development of the current invention.